When you buy the propane quick connect, it will have a shutoff valve built into it. Check the size of the inlet on the female connector. It likely will be 3/8". You need a black 1/2" x 3/8"(or whatever size the connector is) bell reducer and a black short 3/8" nipple. Remove the cap, attach the reducer, then the nipple, then the connector. Be sure to use pipe dope or thread tape on the joints. The connector should have a dust plug included. Be sure to insert it into the connector when not in use to keep out the critters, dirt, and whatever else. When you are done with the assembly, mix some liquid dish soap and water in a 1:10 ratio. Turn the gas on at the tanks and brush the soap solution on the joints to check for leaks. You could also take the trailer to a good RV repair shop and have them perform a manometer test on the LP system to check for leaks if you are uneasy about it.